1. Field of the Invention
One disclosed aspect of the embodiments relates to the technical field of a charged particle beam optical system for use in an apparatus using a charged particle beam, and in particular, to a charged-particle beam lens for use in an exposure apparatus.
2. Description of the Related Art
Electron-beam exposure apparatuses use an electro-optical device for controlling the optical characteristics of an electron beam. There are two types of electron lens, that is, an electromagnetic type and an electrostatic type. The electrostatic type is suitable for size reduction because there is no need to provide a coil core, as compared with the electromagnetic type.
On the other hand, a multibeam system in which a pattern is drawn with a plurality of electron beams without using a mask is one known electron-beam exposure technique. Since the number of beams in the multibeam system corresponds to the number of arrays of electron lenses disposed in the exposure apparatus, a higher array density is required to enhance the throughput.
The electrostatic charged particle lens requires insulating properties (high withstand voltage performance) between electrodes because voltage is applied between the electrodes. To enhance the withstand voltage performance of a charged-particle beam lens, a known method prevents charging of the surface of an insulator sandwiched between electrode substrates by disposing a high-resistance material on the inner wall of the insulator substrate sandwiched between electrode substrates to electrically connect the electrode substrates (see Japanese Patent Laid-Open No. 2001-118491). Another known configuration in a field other than the charged-particle beam lens is a configuration in which a spacer of an electron beam device is covered with a high-resistance film (see Japanese Patent Laid-Open No. 2000-311633).
As the throughput of exposure apparatuses and the definition of exposure patterns have further increased, a higher electric field is required for charged-particle beam lenses. However, there may be a case where conventional charged-particle beam lenses sometimes have insufficient dielectric withstand voltage performance, thus causing discharge. It is clarified that this discharge is caused by the electric field concentration at interfaces between the electrodes and the high-resistance film, as described below, not by charging of the surface of the insulator due to scattered charged particles, disclosed in Japanese Patent Laid-Open No. 2001-118491. The electrostatic type charged-particle beam lens in which a cathode and an anode are electrically connected together by a high-resistance film sometimes generates an oxide film at interfaces between the electrodes and the high-resistance film due to exposure to the atmosphere during a manufacturing process and maintenance of the apparatus. When an electric field is applied between the electrodes, the electric field is concentrated to the interfaces due to high resistance and poor connection of an oxide film portion generated at the interfaces, thus causing discharge due to dielectric breakdown.